1. Field of the Invention
This invention relates generally to the manufacture of slide fasteners from an elongate stringer chain and more particularly to a method of and an apparatus for metering the length of such a stringer chain to be fed and finished into individual slide fastener products.
2. Prior Art
Means have been proposed to mechanically meter an elongate continuous stringer chain to give selected individual lot lengths which are to be finished into slide fastener products. Such known metering means essentially comprises an encoder operatively associated with a feed roller unit in the path of feed of the stringer chain, the output of the encoder being computed to control the length of the stringer chain. This prior art has a drawback in that it is difficult to make accurate metering of the stringer chain in motion due to slippage between the feed rollers and the stringer chain and further due to elongation of the stringer chain while in transit.
Japanese Laid-Open No. 62-84705 discloses an improved means of advancing and stopping a stringer chain at a predetermined position, which means relies on counting the number of coupling elements on the stringer chain. Such positioning means however fails to account for discrepancies in an element-to-element pitch or spacing between adjacent coupling elements which may arise out of the switching between different manufacturing apparatus or between different stringer chain lots and further out of elongation of the stringer chain during feed movement, and therefore poses a problem in accurate and uniform metering function.